Modeling of thermomechanical response of porous shape memory alloys

Shape memory alloys (SMAs) have emerged as a class of materials with unique thermal and mechanical properties that have found numerous applications in various engineering areas. While the shape memory and pseudoelasticity effects have been extensively studied, only a few studies have been done on the high capacity of energy dissipation of SMAs. Because of this property, SMAs hold the promise of making high-efficiency damping devices that are superior to those made of conventional materials. In addition to the energy absorption capability of the dense SMA material, porous SMAs offer the possibility of higher specific damping capacity under dynamic loading conditions, due to scattering of waves. Porous SMAs also offer the possibility of impedance matching by grading the porosity at connecting joints with other structural materials. As a first step, the focus of this work is on establishing the static properties of porous SMA material. To accomplish this, a micromechanics-based analysis of the overall behavior of porous SMA is carried out. The porous SMA is modeled as a composite with SMA matrix, which is modeled using an incremental formulation, and pores as inhomogeneities of zero stiffness. The macroscopic constitutive behavior of the effective medium is established using the incremental Mori-Tanaka averaging method for a random distribution of pores, and a FEM analysis of a unit cell for a periodic arrangement of pores. Results from both analyses are compared under various loading conditions.